Institut de Chimie Moléculaire et des Matériaux d'Orsay

Laboratoire d'Etude des Matériaux Hors Equilibre - LEMHE

Functional Oxides

Staff :

Team leader :

Pr. Nita Dragoe    

Assist. Prof :

Dr. David Berardan

Post-doc :

Dr. Lin Pan
  Dr. Nghi Pham    

Technician :

Céline Byl

Ph’D students :

Céline Barreteau
      Thi-Than-Xuan Vo

Our activities are focused on functional oxide materials, with main interest in thermoelectricity and superconductivity.

We also study the influence of the oxygen stoichiometry and of the nanostructuration on these materials properties.

 

At room temperature, « perfect » compounds regarding their stoichiometry are scarce, if they even exist. Reactions between the materials surface and the surrounding atmosphere, and more especially with oxygen, lead to small stoichiometry changes, even at room temperature. These minor changes will often induce a strong evolution of the materials physical properties. Therefore, we are interested in the study of the correlations between the real oxygen stoichiometry of oxide materials and their physical properties, in order to design improved materials, and especially thermoelectric materials.

Recently, we have shown that:

  • The oxides electrical transport properties are strongly influenced by the surrounding atmosphere at high temperature, which was known for long,

but also that:

  • The properties evolution can occur very fast, and that the transport properties measurement itself can be strongly influenced by the measuring conditions.

This latest results explains the huge dispersion of the data reported in the literature for some oxide materials, including for example ZnO. It is noteworthy that the precise measuring conditions are often not described in the papers, but that most commercial measurement devices are designed to be used under vacuum or inert atmosphere, although oxide materials are not always stable in these measurement conditions. Therefore, we have designed our own measurement facilities so that they can be used under controlled atmosphere.

For example, the following figure shows the thermopower of a thermoelectric oxide as a function of the temperature and the surrounding atmosphere. It is noteworthy that the evolution that occurs when changing the atmosphere is very fast.

This project was supported by Univ. Paris-Sud through a “BQR” funding, as well as by the Division de la Recherche of the Faculty.

References

N. Dragoe, D. Berardan, C Byl, On the high temperature transport properties of thermoelectric oxides,  Physica status solidi a 2011, 208, 140 [PDF]

 

 

 
21 février, 2013